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Full text of "Text Book Of Mechanical Engineering"

Appendix II.

805

understood from Fig. 769, A being the main cylinder and B B the
lifting rams.

Both methods have since been adopted satisfactorily, and two-
things have to be noted: (i) that immense rigidity of framing
is required on account of the heavy pressures, 2 or 3 tons per
square inch, and (2) that the difficulty of keeping valves and
packings water-tight causes some makers to dispense with the
former altogether. A very useful modern press, designed by the
late Mr. Tweddell, is shewn at T, plate xv, facing p. 318, where
the absence of pillars is a convenient arrangement

Cold drawing of metals has  long been practised in the
manufacture, of wire from more or less plastic materials, a hard

steel plate being drilled with a series of holes of gradually de-
creasing size, through which the material is passed in succession
from largest to least The principle is also applied to plates of
the same materials, which are stamped by a regular series of dies
until the required shape, often much removed from the original
condition, is attained Between every 'draw/ or nearly so, it is
usual to anneal the work, for such forced flow of material produces